I don't think ISPs are very interested in solving this problem, and the solution I described isn't what people expect from either mod_perl or CGI, so it would be hard to market.

I do use this when doing development on mod_perl modules. If you avoid loading the module you're working on before forking, you can test it without ever doing restarts this way, and it works for mod_perl-specific modules that can't be run under CGI.